Synthesis of procyanidin B3 and its anti-inflammatory activity. the effect of 4-alkoxy group of catechin electrophile in the Yb(OTf)(3)-catalyzed condensation with catechin nucleophile.

Yb(OTf)(3)-catalyzed equimolar condensation of the benzylated catechin with various 4-alkoxy catechin derivatives was studied. In particular, the reaction using 4-(2''-ethoxyethoxy)flavan derivative gave good yield with excellent stereoselectivity. The condensed product was successfully converted to procyanidin B3 (1). The anti-inflammatory effect of procyanidin B3 (1) on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced inflammation of mouse ears was examined. The anti-inflammatory activity of 1 was stronger than that of indomethacin and glycyrrhetinic acid, the normally used anti-inflammatory agents.